The ultimate aim of this research is to improve our understanding of physical mechanisms of normal and disordered voice production. Using a variety of laboratory models of vocal fold vibration (physical models, excised human larynx modes, in vivo canine laryngeal models), the proposed research will investigate mechanisms of regular and irregular vibration by quantifying the medial surface dynamics of the vocal folds. Access to the medial surface will be obtained through means a hemi-larynx methodology, and high-speed, stereoscopic, digital imaging. Medial surface dynamics captures the propagation of the mucosal wave, the existence of which is generally understood to be a necessary condition of phonation. With access to medial surface dynamics, spatio-temporal analyses will reduce the data to essential dynamics to help disclose physical mechanisms of vibration. With this focus on medial surface dynamics, the following Specific Aims will be pursued: (1) Identify and characterize the phonation types which occur as a function of glottal adduction, (2) Identify and characterize the phonation types which occur as a function of viscoelastic and geometric changes in the body/cover structure of the vocal folds, (3) Identify and characterize the phonation types which occur as a function or source-resonator coupling, (4) Identify and characterize the phonation types which occur as a function of left-right asymmetries, (5) Clarify the degree to which an endoscopic view of the vocal folds can or cannot disclose physical mechanisms of normal and disordered voice production. Contrast the information regarding physical mechanisms of vibration that can be extracted from acoustic spectrograms, spatio-temporal analyses of the superior surface of the vocal folds, and spatio-temporal analyses of the medial surface of the vocal folds.